The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The aircraft turbojet engines generate significant noise pollution. There is a strong demand aiming at reducing this pollution, and even more so as the turbojet engines used become more and more powerful. The design of a nacelle surrounding a turbojet engine contributes for a large part to the reduction of this noise pollution.
In order to further improve the aircrafts' sound performances, the nacelles are equipped with sound absorbing panels aiming at reducing the noise transmission generated by the turbojet engine.
Generally, such sound absorbing panels are installed on the nacelle surrounding the turbojet engine in inlet and/or outlet of the fan duct of the turbojet engine.
A nacelle for an aircraft turbojet engine has typically several functionalities such as to maintain the turbojet engine to an attachment engine strut connected to a wing of the aircraft, to reverse the thrust of the turbojet engine, or furthermore, to integrate noise attenuating and de-icing devices.
During a phase of flight of an aircraft, it is common that the climatic conditions in altitude cause a frost build-up in different spots of the aircraft. Frost may for example be formed on the nacelle of the turbojet engine, including the leading edge of said nacelle. Such frost build-up is unacceptable, because it can cause changes in the aerodynamic profile of the nacelle, or can also damage the turbojet engine in the case of extracting blocks of ice formed on the air inlet lip of the nacelle.
It is therefore imperative to equip the nacelle of the turbojet engine with a device preventing the frost and ice build-up on the nacelle.
Such devices are, in known manner, carried out by sampling the hot gases in the compressor of the turbojet engine or by producing them by compression or heating, and by redirecting them on the surface of the nacelle which can be affected by the ice build-up.
A recurring problem is related to the cohabitation of sound absorbing and de-icing devices. Indeed, in general, a sound absorbing panel is located close to the air inlet lip of the nacelle; this has the effect of limiting the functional part of the de-icing device in areas of the nacelle which are not covered by the sound absorbing panel.
EP 0 913 326 provides a solution to this problem through the installation of a “Picolo” tube within the air inlet lip of the nacelle or a system of rotating movement of the de-icing fluid, allowing the injection of a de-icing fluid through the alveolar core structure to form the intermediate layer of the sound absorbing device.
EP 1 103 462 also describes a system of rotating movement of a de-icing fluid, “swirl” tube, which delivers a de-icing fluid passing then through a alveolar core structure of a device of sound processing.
A common drawback with these solutions is that the sound processing is disturbed by this fluid, which causes a malfunction of the sound absorbing device.
We also know U.S. Pat. No. 3,933,327, which provides a de-icing device for an air inlet of a nacelle of a functional turbojet engine at the sound processing zone, thanks to openings provided in the thickness of the alveolar core structure of the sound processing device, these openings allowing to facilitate the passage of a hot gas through the cells of said structure. A major drawback of this solution is the complexity of manufacturing the sound processing device. In fact, the alveolar structure is complex to implement insofar as intended to let the hot gas pass must be implemented on each cell wall.
Finally, FR 2 820 715 describes sound attenuating means formed by a plurality of unconnected islands, between which a hot pressurized fluid flows from a de-icing system of the cowl of air inlet of a turbojet engine. According to these method and device, the performance of the de-icing device is not affected by the sound processing device. However, first of all, the performances of the sound attenuating means are sharply reduced because the sound processing surface is decreased because of corridors arranged in the air inlet lip for the passage of hot pressurized fluid. Then, the integration of sound attenuating means is difficult to accomplish because it is necessary to provide a corridor for hot fluid circulation between two strips of alveolar core structure.